Apparatus for forming a homogeneous intensity distribution with bright or dark edges

Abstract

A beam homogenizer for transforming a beam of laser-radiation into a flat-top intensity distribution having brighter or darker edges comprises a first lens array, a second lens array, and a positive lens. The first lens array includes a plurality of lens elements that are separated by gaps having no optical power. Brighter or darker edges are produced by selecting a distance between the first and second lens arrays that is less than or greater than the focal length of lens elements in the second lens array.

What is claimed is: 
     
       1. A beam homogenizer, comprising:
 a first lens array, the first lens array having a plurality of identical lens elements, each lens element of the first lens array having a focal length F 1 , neighboring lens elements of the first lens array being separated by a gap, the gap having no optical power, each gap having a common width; 
 a second lens array, the second lens array having a plurality of identical lens elements, each lens element of the second lens array having a focal length F 2 , the first lens array and the second lens array being separated by a distance F 2 ±δ, δ being a distance that is less than 20% of F 2 ; and 
 a positive lens located on an optical axis having a focal length F 3 , the first lens array, the second lens array, the positive lens, and an illumination plane being arranged in that order along the optical axis, the illumination plane located a distance F 3  from the positive lens; 
 wherein F 1 , F 2 , F 3 , and δ are selected such that a ray incident on a lens element of the first lens array at a distance X 1  from a center of the lens element is projected onto the illumination plane at a distance X 2  from the optical axis of 
 
       
         
           
             
               
                 
                   
                     - 
                     
                       X 
                       1 
                     
                   
                   ⁢ 
                   
                     F 
                     3 
                   
                 
                 
                   F 
                   2 
                 
               
               ⁢ 
               
                 
                   ( 
                   
                     1 
                     ∓ 
                     
                       δ 
                       
                         F 
                         1 
                       
                     
                   
                   ) 
                 
                 . 
               
             
           
         
       
     
     
       2. The beam homogenizer of  claim 1 , wherein the first lens array and the second lens array are separated by a distance F 2 +δ that is more than F 2 . 
     
     
       3. The beam homogenizer of  claim 1 , wherein the first lens array and the second lens array are separated by a distance F 2 −δ that is less than F 2 . 
     
     
       4. The beam homogenizer of  claim 1 , wherein δ is less than 10% of F 2 . 
     
     
       5. The beam homogenizer of  claim 4 , wherein δ is less than 5% of F 2 . 
     
     
       6. The beam homogenizer of  claim 1 , wherein the gap between neighboring lens elements of the first lens array is an empty gap or air gap. 
     
     
       7. The beam homogenizer of  claim 1 , wherein the gap between neighboring lens elements of the first lens array is made of the same material as the lens elements of the first lens array. 
     
     
       8. The beam homogenizer of  claim 7 , wherein the material that the gap and the lens elements of the first array are made from is a transparent glass or polymer. 
     
     
       9. The beam homogenizer of  claim 1 , wherein the gap between neighboring lens elements of the first lens array fixedly connects the neighboring lens elements. 
     
     
       10. The beam homogenizer of  claim 1 , wherein the gap between neighboring lens elements of the first lens array is in the form of a slab having plane parallel faces. 
     
     
       11. The beam homogenizer of  claim 1 , wherein the gap between neighboring lens elements of the first lens array is in the form of a wedge having plane but not parallel faces. 
     
     
       12. The beam homogenizer of  claim 1 , wherein an image having a repeated pattern of broader and narrower bands located in an image plane at a distance F 2  from the second lens array is imaged onto the illumination plane. 
     
     
       13. The beam homogenizer of  claim 1 , wherein the first lens array is configured and arranged to be longitudinally translated parallel to the optical axis. 
     
     
       14. A beam homogenizer, comprising:
 a first lens array, the first lens array having a plurality of identical lens elements, each lens element of the first lens array having a flat center portion and curved outer portions, the center portion having no optical power and the outer portions having a focal length F 1 ; 
 a second lens array, the second lens array having a plurality of identical lens elements, each lens element of the second lens array having a focal length F 2 , the first lens array and the second lens array being separated by a distance not equal to F 2 ; and 
 a positive lens located on an optical axis having a focal length F 3 , the first lens array, the second lens array, and the positive lens being arranged in that order along the optical axis. 
 
     
     
       15. The beam homogenizer of  claim 14 , wherein the first lens array is configured and arranged to be longitudinally translated parallel to the optical axis. 
     
     
       16. A beam homogenizer for laser radiation, comprising:
 a first lens array, the first lens array having a plurality of identical lens elements, each lens element of the first lens array having a focal length F 1 , neighboring lens elements of the first lens array being separated by a gap, the gap having no optical power, each gap having a common width; 
 a second lens array, the second lens array having a plurality of identical lens elements, each lens element of the second lens array having a focal length F 2 , the first lens array and the second lens array being separated by a distance F 2 ±δ, δ being a distance that is less than 20% of F 2 ; and 
 a positive lens having a focal length F 3 , the laser radiation propagating through the lens elements and the gaps of the first lens array, through the second lens array, through the positive lens, and onto an illumination plane in that order, the illumination plane located a distance F 3  from the positive lens; 
 wherein laser radiation propagating through the lens elements of the first lens array has a different magnification in the illumination plane than laser radiation propagating through the gaps of the first lens array; 
 wherein F 1 , F 2 , F 3 , and δ are selected such that a ray incident on a lens element of the first lens array at a distance X 1  from a center of the lens element is projected onto the illumination plane at a distance X 2  from the optical axis of eδ/F 1 . 
 
     
     
       17. The beam homogenizer of  claim 16 , wherein the first lens array and the second lens array are separated by a distance F 2 +δ that is more than F 2 . 
     
     
       18. The beam homogenizer of  claim 16 , wherein the first lens array and the second lens array are separated by a distance F 2 −δ that is less than F 2 . 
     
     
       19. A beam homogenizer for laser radiation, comprising:
 a first lens array, the first lens array having a plurality of identical lens elements, neighboring lens elements of the first lens array being separated by a gap, the gap having no optical power, each gap having a common width; 
 a second lens array, the second lens array having a plurality of identical lens elements, each lens element of the second lens array having a focal length F 2 , the first lens array and the second lens array being separated by a distance not equal to F 2 ; and 
 a positive lens having a focal length F 3 , the laser radiation propagating through the lens elements and gaps of the first lens array, through the second lens array, through the positive lens, and onto an illumination plane in that order, the illumination plane located a distance F 3  from the positive lens, the laser radiation on the illumination plane transformed into a homogenized intensity distribution having brighter or darker edges in an otherwise uniform intensity distribution.